Default targets don't work correctly when element-path is "."

Summary

When element-path of a project is configured to ., i.e. the project directory, our logic for finding default elements breaks down. Since we stage junctions in .bst directory, the current logic tries to find all .bst files inside the junction, which is not expected. It's worse than that because it mangles the path and then tries to look for those elements in bst directory instead of .bst, and fails subsequently.

Steps to reproduce

1. Create a project with element-path: ..
2. Create a junction on some other project.
3. Run bst show, everything should be fine this time as we won't have .bst directory to begin with.
4. Run bst show again, watch it fail, as this time bst tries to find elements in the staged junctions.

What is the current bug behavior?

bst show or any other commands fail on all subsequent runs when no target is specified.

What is the expected correct behavior?

bst show and other commands should not attempt to find elements from staged junctions, and not error out in either case.

Relevant logs and/or screenshots